1. Field of the Invention
The present invention relates to Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiplexing Access (OFDMA) technologies. More particularly, the present invention relates to a method for mapping data, a method for de-mapping data, a transmitting device and a receiving device.
2. Description of the Related Art
OFDM technology is a type of communication technology that more effectively transmits information using channels. That is, OFDM technology utilizes multiple parallel subcarriers, which may also be referred to as subcarrier frequencies, that transmit low-rate data, to achieve communication of high-rate data. A technical point of the OFDM technology is as follows. The transmitting bandwidth of a channel is divided into several sub-frequency bands. The transmitting end transmits data information in parallel with subcarriers that are mutually orthogonal in each sub-frequency band, and the receiving end extracts the data information transmitted in parallel utilizing orthogonality of each subcarrier.
The OFDM technology has been applied in many communication systems successfully. For example, the OFDM technology is used as the air interface for Data Audio Broadcast (DAB) and Digital Video Broadcast (DVB) established by European Telecommunications Standards Institute (ETSI). The OFDM technology is also adopted by the Institute of Electrical and Electronics Engineer's (IEEE) wireless Local Area Network (LAN) standard IEEE 802.11 and wireless Metropolitan Area Network (MAN) standard IEEE 802.16. Besides, with continuous updating of communication services technology, various new service requirements continuously emerge and the OFDMA technology continues to be widely used. The OFDMA technology, which is based on the OFDM technology, divides different resource blocks in time-frequency resources to form different sub-channels, and allocates different services for different sub-channels, to achieve greater flexibility.
Although the OFDM technology has many advantages, it is very sensitive to frequency-offset error. When a frequency-offset error occurs, data that is transmitted with various subcarriers that are originally mutually orthogonal becomes interference to other subcarriers. Thus, Inter-Carrier Interference (ICI) is generated. More particularly, when a mobile station receives signals from different base stations, different frequency-offset errors will cause more complex interference among subcarriers. In addition, when a mobile station moves with a high speed, a Doppler spread may also lead to interference among subcarriers.
Several solutions for the ICI problem have been proposed, for example, adopting balancing technology, spread spectrum technology, etc. However, implementation of these technologies is very complex.
Accordingly, there is a need for an improved apparatus and method for mapping and transmitting data so as to reduce interference among subcarriers.